1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Cyclist coasting down a hill cons. of energy

  1. Apr 21, 2013 #1
    1. The problem statement, all variables and given/known data
    A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?


    2. Relevant equations
    EK=1/2 mv2
    EG=mgh
    P=W/T


    3. The attempt at a solution
    I tried the question and this is what I got but I'm answer if this is right... not sure if there's a Force of friction though because I read the question and assumed there isn't any force of friction... but I'm unsure... :uhh:

    P=W/T
    P=-WGΔdcos180°/T
    P=-WGvcos180°
    P=-mgsin7.0°(5.0)cos180°
    P=-(75)(9.8)sin7.0°(5.0)cos180°
    P=448W
     
  2. jcsd
  3. Apr 21, 2013 #2
    Well if the cyclist goes down the hill with constant speed, then there must be some kind of force that's stopping him from accelerating, so you should account for it accordingly.
     
  4. Apr 21, 2013 #3

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    hi totallyclone! :smile:
    he couldn't coast (at a steady speed) if there wasn't friction, could he? :wink:
     
  5. Apr 21, 2013 #4
    so.....THERE'S FRICTION!!?!??
     
  6. Apr 21, 2013 #5

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    yup!!! :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted